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Book/Report | FZJ-2019-04486 |
1998
Forschungszentrum Jülich, Zentralbibliothek, Verlag
Jülich
Please use a persistent id in citations: http://hdl.handle.net/2128/22623
Report No.: Juel-3582
Abstract: This thesis deals with two fundamental questions concerning magnetic data storage. The first question addressed, is: Does a magnetic exchange coupling exist between ferromagnetic layers separated by a semiconducting interlayer. Using SPLEED and MLD in photoemission, a ferromagnetic coupling between Fe layers separated by a ZnSe layer has been observed. The coupling strength decreases exponentially with increasing interlayer thickness, in agreement with theoretical predictions. Uncoupled, thin Fe layers on ZnSe below 10 $\mathring{A}$ thickness do not show an in plane magnetic signal which is explained as an anisotropic effect. This has been utilized as a very sensitive means to measure the coupling to the buried Fe layer in Fe/ZnSe/Fe. The second part of this thesis deals with the magnetic response of a ferromagnetic material on an ultrafast optical excitation with f-sec laser pulses. Two magnetic relaxation channels have been observed, one on a sub p-sec time scale, and the other on a time scale of several hundred p-sec. The fast relaxation is attributed to the creation of Stoner excitations and a decrease of the local magnetic moment, the slow one to magnon-phonon coupling and a reduction of the long range magnetic order.
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